The use of portable electronic devices, electric vehicles, space and aircraft system, and even stationary power supplies has caused a large demand for high quality batteries. Lithium-ion batteries are frequently used because of their high energy densities and long lifetimes. Nevertheless, a long charging time continues to be a problem in applications where minimizing the charging time is important.
Constant Current-Constant Voltage
Conventional constant current-constant-voltage charging of lithium-ion batteries has two stages. First, the battery is charged at a constant current until the voltage reaches an upper limit, e.g., 4.1 or 4.2 volts. Second, the battery is charged at a constant voltage until the current reduces to about 3% of its rated value. The time required for the constant current is about one hour, and the time the constant voltage stage is about two hours for fulfill the residual 20% of the entire capacity of the battery.
Charging battery at a higher current or voltage can lead to lower battery capacity, and a shorter battery life, in addition to safety problems, e.g., overheating the battery.
Pulse Charging
Pulse charging can reduce the charging time. Pulse charging uses a high current charging, followed by a relaxation. During the high current charging, lithium ions are electrochemically reduced and intercalated into a graphite electrode matrix. If the current density is too high, then the reduced lithium cannot be fully intercalated. This means that the reduced lithium accumulates at an interface of the battery, which limits the charging rate.
There have been many efforts on modeling the internal processes of lithium-ion batteries. Those prior art models start from different perspective but all aim for a simplistic but accurate simulation of batteries. Such models include empirical models, electrochemical models, electrical-circuit models, and stochastic models.
Another class of models is analytical. Those models also describe the nonlinear effects inside of the battery, but the models do not have such clear physical meanings as electro-chemical models, or electrical-circuit models.
The conventional models simulate discharging processes.